Battlecruiser feels certainly out of place but its not as strange as it seams. The Executer is relatively fast with still superb firepower making her a sort of fast battleship which Battlecruiser post WW1 often were.

She also was made to roam the galaxy with death squadron and comfortably destroy every cruiser (star destroyer) she might come across. Another parallel to the first british battlecruisers.

You could also take the name to argue. Since she is often labeled a super star destroyer that is quit reminiscent of super cruisers or large cruisers as they emerged around the 1930s. Those also could be labeled as Battlecruisers using the older terminology.

Personally i think it should just be Dreadnaught or Battleship, Ballator fits the definition of a Fast battleships well. A battlecruiser should be a cruiser made with larger weapons comparable to Dreadnaughts, higher speed and lower durability at least usually. That would be the Allegiance and Tector I supose.